Exothermic composition for use in steelworks and in foundries

ABSTRACT

THIS EXOTHERMIC COMPOSITION CAN BE USED IN CASTING MOLTEN METALS IN STEELWORKS AND IN FOUNDRIES SO AS TO DELAY SOLIDIFICATION AND TO FILL UP THE CAVITIES CAUSED BY THE SHRINKAGE OF THE METAL DURING SOLIDIFICATION. IT CONTAINS IN A KNOWN MANNER ALUMINUM, AT LEST ONE OXIDISING AGENT AND AT LEAST ONE FILLER. IT ADDITIONALLY CONTAINS A SOLID EASILY COMBUSTIBLE CARBONACEOUS MATERIAL IN A FINELY DIVIDED STATE. THIS MATERIAL CAN BE PAPER OR PLASTIC. IN CASE OF PAPER, THE PROPORTION AS USED IS AT LEAST 5%. THIS PROPORTION IS COMPRISES BETWEEN 0.2 AND 5% IN CASE OF PLASTIC. THE COMPOSITION ADVANTAGEOUSLY CONTAINS FINE PARTICLES OF A COMPOSITE CONSISTING OF A FILM OF ALUMINUM DEPOSITED ON A SUPPORT OF A SOLID EASILY COMBUSTIBLE CARBONACEOUS MATERIAL SUCH AS PAPER OR PLASTIC.

United States Patent 3,720,552 EXOTHERMIC COMPOSITION FOR USE INSTEELWORKS AND IN FOUNDRIES Simon Lustigue, 28 Avenue Leman, Lausanne,Switzerland No Drawing. Filed Mar. 15, 1971, Ser. No. 124,508 Int. Cl.C06b 19/02 US. Cl. 1493 Claims ABSTRACT OF THE DISCLOSURE Thisexothermic composition can be used in casting molten metals insteelworks and in foundries so as to delay solidification and to fill upthe cavities caused by the shrinkage of the metal during solidification.-It contains in a known manner aluminum, at least one oxidising agentand at least one filler. It additionally con- The present inventiongenerally relates to the technique of casting molten metals insteelworks or in foundries. It is well known to use compositions whichare exothermic and/or insulating and/or refractory when casting moltenmetals, so as to delay solidification. Thus, in the case of castingsteel into ingot moulds, the upper part of the steel charge contained inthe ingot is kept liquid so as to fill up the cavities caused by theshrinkage of the steel during solidification, thus producing acorresponding reduction in the rejected top end of the ingot. Infoundries, a feedhead, acting in a similar manner, is kept in the liquidstate so as to yield sound castings.

Such compositions are employed in various forms, either as a coveringpowder which is poured onto the metal after casting, or in the form of alining applied to the walls of an ingot mould, or in the form of asleeve or the like. Such a lining can be produced by attachingprefabricated sheets of lining or by tamping powder into a casing.

The known exothermic compositions contain aluminum in the pure stateand/or in the form of aluminum dross, fluorides, oxidising agents suchas chlorates, iron oxide, manganese dioxide and the like, and generallyone or more fillers such as alumina, sand, chamotte, perlite and thelike, depending on the operating conditions and on the desired results.

One object of the invention is to provide a new exothermic compositionwhich can be used in steelworks and foundries when casting metals.

Another object of the invention is to provide an exothermic compositionwhich can be used during the casting of metals, of the type whichcontains, in a known manner, aluminum or an aluminum compound, at leastone oxidising agent and at least one filler, characterised in that itfurthermore contains a solid easily combustible carbonaceous material ina finely divided state. This material can be paper or a plastic.

According to the invention, if this composition contains paper, theamount of paper is at least 5% relative to the total composition.

If this composition contains a plastic, it is advisable for the amountof plastic to be between 0.2 and 5%. The said composition can alsosimultaneously contain paper and a plastic. The investigations whichhave resulted in the invention have shown that such a proportion ofpaper or plastic, in a finely divided state, in the exothermiccomposition makes it possible to achieve more uniform combustion ofthis. composition.

It is in fact known that under the influence of the heat provided by themetal, for example by liquid steel, which is at about 1600 C. at thetime of casting, the aluminum and the oxidising agents react so as toproduce an additional evolution of heat. This reaction is well known. Itforms the basis of aluminothermy. The investigations indicated abovehave shown that this reaction by combustion is rendered more uniformthrough the presence of paper and/or of plastic. Furthermore, theincorporation of paper and/or of plastic in the composition makes itpossible to obtain markedly lower densities, which can for example be aslow as 0.35-0.40.

According to an example given without implying a limitation, thecomposition can contain more than 15%, and in particular about 20%, ofpure aluminum, or an amount of aluminum dross representing about 20% ofaluminum, 15 to 20% of oxidising agents, for example chlorates, ironoxide, manganese dioxide, fluorides and the like, 50 to 65% of fillerssuch as alumina, sand, chamotte, perlite and the like, and at least 5%of paper in a finely divided state. At least a part of the paper of thiscomposition can be replaced by the plastic. However, in this case theproportion of plastic will generally be less than 5%.

It is already known to incorporate paper or equivalent cellulosic fibresinto refractory or insulating linings used in steelworks. On contactwith the liquid steel, the paper or the fibres undergo combustion andthus allow the lining to be disintegrated after the ingot hassolidified. In the composition which forms the subject of the invention,the paper and/or the plastic fulfill an additional function because thepresence of a proportion of paper and/or of plastic in a finely dividedstate in the composition ensures, in an intrinsically noteworthy manner,that the combustion is more uniform. Furthermore, the density of thecomposition is reduced.

The composition according to the invention can be used in the form of acovering powder intended to be poured over the liquid metal immediatelyafter casting, or in the form of a powder intended to be tamped orpressed into a casing, for example inside an ingot mould, or in the formof a pulverulent composition which can be mixed with one or moresuitable binders so as to manufacture lining elements or exothermicfeedheads in a manner which is in itself known.

The composition according to the invention can be prepared simply bymixing the constituents of which it consists. These constituents areused in a manner which is known for the production of compositions ofthis type, in the form of powders or in a finely divided state, and, forexample, the paper and/or the plastic, especially in the form of scrap,can be chopped or ground so as to reduce them to a suitable particlesize, allowing them to be well distributed in the entire composition.

However, a different embodiment consists of starting from an alreadyexisting aluminum-paper or aluminumplastic composite.

It is known to deposit a film of aluminum on a paper or plastic supportfor certain industrial or commercial uses, for example for packagingcertain commercially supplied products. In industry, there existsrelatively large amounts of scrap of a composite consisting of analuminum-paper laminate or aluminum-plastic laminate. Attempts havealready been made to recover the aluminum from this composite, in viewof the fact that this material is expensive. The solutions proposed havefor example consisted of burning the said composite so as to destroy thepaper or plastic support and thereafter to recover the aluminum.However, this combustion changes the properties of the aluminum. Theresult is no better if attempts are made to destroy the paper or theplastic by chemical means.

The invention provides a particularly simple means of recovery, whichmakes it possible to use to optimum effect the amounts of wastealuminum-paper or aluminum-plastic composite which exist in industry.According to the invention, this waste composite is ground so as toreduce it to a sufficiently small particle size for it to beincorporated into a pulverulent composition such as that describedabove, and the said particles are incorporated into such a composition.

Certain composites, of the type in question, contain about 30 to 35% byweight of aluminum and 65 to 70% by weight of paper. Other compositescomprise an aluminum film deposited on an extremely thin plastic supportfilm, so that this composite contains, for example, 65 to 70% by weightof aluminum. The incorporation of the finely divided product obtained bygrinding such composites thus introduces into the composition at least apart of the aluminum required in the exothermic compositions of thistype and a not insignificant proportion of paper or of plastic.

Furthermore, it is possible to establish that the grinding carried outin fact does not separate the aluminum from the paper or from theplastic and that, in a certain number of particles, aluminum and paperor plastic are simultaneously present, even though these constituentscannot be detected with the naked eye if the size of the particles areexpressed in microns, as is the case for powders, so that the paper isperfectly distributed in the mass of the composition and providesoptimum uniformity of combustion.

According to yet a further characteristic, aluminumpaper oraluminum-plastic composites in a finely divided, chopped or ground,state used in the exothermic composition which forms the subject of theinvention are of the type in which the aluminum film is at least partlyprotected by printing, by application of a varnish or in some similarmanner.

In fact, the greater is the contact surface between the aluminum and theoxidising agents which provide oxygen and which are present in theexothermic composition, the faster is the exothermic reaction betweenthe aluminum and these oxidising agents, and the greater is the amountof heat evolved per unit time, thereby allowing higher temperatures tobe obtained. Conversely, the lower is the contact surface, the slower isthe reaction and the lower is the temperature reached.

The heat evolved at the time of reaction is partly transferred to theliquid steel so as to replace the calories lost on leaving the ladlewhen casting into the ingot mould, but the greater part of the heatproduced is furthermore transferred to the constituents which surroundthe thermogenic materials consisting of the aluminum and the oxidisingagents, especially to the insulating and refractory constituents whichare intended to preserve this heat. It is easily understood that themore rapidly the amount of heat produced by a given charge of aluminumand oxidising agents is involved, the higher is the temperature reachedby the steel and by the abovementioned insulating and refractoryconstituents, so that optimum preservation of the heat is ensured.

In the case of aluminum shot or aluminum powder used without specialprecautions, a layer of oxide is found to be present on the surface ofthe aluminum particles, which interferes with the almost pure aluminumemployed coming into contact with the oxidising agents and which hencecounteracts maximum evolution of heat. This is also the case for scrapaluminum-paper and aluminum-plastic composites in a finely dividedstate, for example in the form of fibres or of extremely narrow strips.The presence of a varnish, for example, prevents the oxidation of thesurface of the aluminum. At the time of contact with the steel, thisfilm of varnish is removed under the influence of heat, and the aluminumis directly in contact with the oxidising agents, which allows a rapidreaction and maximum evolution of heat within a very short space oftime, with the advantages of a high temperature which result therefrom.

This result is particularly discernible in the case where the composite,cut into fibres or extremely thin strips, is used in the manufacture ofexothermic feedhead slabs. The experiments carried out show that in sucha case an improvement of about 20% in the results obtained is achieved.

Modifications can be introduced into the embodiments described, withinthe scope of technical equivalence.

What is claimed is:

1. In an exothermic composition for use when casing molten metals,comprising an intimate admixture of fine particles of aluminum, at leastone oxidizing agent, at least one filler, and at least one solid easilycombustible carbonaceous material selected from the group consisting ofpaper and plastic; the improvement in which at least a portion of saidaluminum and at least a portion of said carbonaceous material are in theform of a composite of a layer of aluminum on a layer of saidcarbonaceous material.

2. An exothermic composition as claimed in claim 1, in which saidcomposite is a film of aluminum deposited on a support of saidcarbonaceous material.

3. An exothermic composition as claimed in claim 1, and a protectivefilm on the free surface of the aluminum of said composite.

4. An exothermic composition as claimed in claim 1, in which saidcomposite consists essentially of 30-35% by weight of aluminum and -70%by weight of carbonaceous material.

5. An exothermic composition as claimed in claim 1, in which saidcomposite consists essentially of 65-70% by weight of aluminum and30-35% by weight of carbonaceous material.

References Cited UNITED STATES PATENTS 1,168,061 1/1916 Deppeler 149371,751,550 3/1930 Hyde 14937 3,020,610 2/1962 Rejdak 14937 X 3,050,409 8/1962 Bayer 149-37 X 3,089,798 5/1963 Rejdak 149-37 3,160,537 12/1964Trafton 149-37 3,347,721 10/1967 Iago 14937 X STEPHEN I. LECHERT, JR.,Primary Examiner U.S. Cl. X.R.

